1. Statement of the Invention
This invention relates to cathodic protection of pipelines or the like and more particularly to improvements in the sacrificial anode of the bracelet type for embracing a pipeline or the like for cathodic protection of the pipeline, which improvements minimize or substantially minimize distortion of the anode segments during cooling after casting and also minimize or substantially minimize fracturing of the anode segments during installation about the pipeline. Additionally this invention is concerned with the improved sacrificial anode segment per se, the anode assembly and a method for the preparation of the anode segments.
2. Description of the Prior Art
Semi-cylindrical galvanic anode segments for embracing a pipeline for cathodic protection of the pipeline are known in the prior art and are disclosed in U.S. Pat. No. 3,616,422, reissued as Reissue U.S. Pat. No. 27,529. Although such anode segments give entirely satisfactory results in certain respects, one drawback of such semi-cylindrical segments is their tendency to become distorted during cooling of the metal after casting of the segments and also to fracture during installation about the pipeline, and this was particularly the case with the longer semi-cylindrical segments which are utilized with the larger diameter pipelines. The desideratum is to provide the curved anode segments with a curvature which closely approximates the curvature of the coated pipeline about which the anode segment is to be installed so that the curved segments will fit closely about the pipeline and it was, generally speaking, virtually impossible to cast a curved anode segment every time having a curvature closely approximating the curvature of the pipeline. And this was especially the situation when casting the longer anode segments for use about the large diameter pipelines. When the anode segment does not have sufficient curvature to correspond to that of the pipeline, it is necessary to bend end portions and/or other portions of the segment inwardly by application of pressure to obtain the necessary curvature to conform to and closely fit about the pipeline, and the pressure application required for the bending may result in cracking of the anode segment. Sometimes it is necessary to bend the curved anode segments outward by application of pressure to obtain the necessary curvature to closely fit about the pipeline and this pressure application may also result in cracking of the segment. Cracking of the sacrificial anode metal of the segment is undesirable for the reason a crack or cracks in the sacrificial anode metal may expose the cathodic core metal of the anode, which is embedded within the sacrificial anode metal. Consequently, after installation and exposure of the cathodic core metal to the electrolyte due to the crack or cracks in the anode metal, the anode expends itself of sacrificial anode metal to protect the core metal with the resultant inefficiency and wasting of sacrificial anode metal. Notches have been provided in the aforementioned prior art semi-cylindrical anode segments for promoting cracking at the center of the segment.
The publication "Cathodic Protection of Submarine Pipeline," reprinted from the Federated Metals Digest of the American Smelting and Refining Company, Federated Metals Division, published 1958, discloses a sacrificial anode assembly wherein the anode segments are indirectly connected together by the steel cores of the anodes being welded to steel bands. The major axis of the cores of the anodes are parallel to the major axis of the pipe, and the cores extend from that portion of the anode which are the side edges of the anode.
Heretofore non-arcuate shaped anode segments have been heated and then bent in the heated condition to fit the segment about the shaft housing of a marine propeller. The anode segments were welded to non-anodic housing structural members and were not connected to one another about the housing. The problem is that when the anode segments are of zinc or zinc base alloy the segments tend to crack during the bending at ambient temperature due to the brittle nature of the zinc. Arcuate-shaped anode segments have also been cast heretofore and bolted about the shaft housing of a marine propeller. Again the segments were not connected to one another about the housing.